Re: [PATCH v2] fs: always return zero on success from replace_fd()

On Mon, Aug 04, 2025 at 04:52:29PM +0100, Al Viro wrote:

On Mon, Aug 04, 2025 at 02:33:13PM +0200, Christian Brauner wrote:

...

•   guard(spinlock)(&files->file_lock);
    err = expand_files(files, fd);
    if (unlikely(err < 0))
  

•           goto out_unlock;
  

•   return do_dup2(files, file, fd, flags);
  

•           return err;
  

•   err = do_dup2(files, file, fd, flags);
  

•   if (err < 0)
  

•           return err;
  
  

-out_unlock:

•   spin_unlock(&files->file_lock);
  

•   return err;
  

•   return 0;
  

}

NAK. This is broken - do_dup2() drops ->file_lock. And that's why I loathe the guard() - it's too easy to get confused *and* assume that it will DTRT, no need to check carefully.

To be fair I also got this wrong in my original v2 patch not using guard(). I'll send a fixed version tomorrow.

Thomas